It is a remarkable achievement: that a magazine containing not much apart from crude, and crudely drawn, cartoons, first sold in a Newcastle pub for 20p (30p to students), could be selling, within a few years and with the same editorial team, more than a million copies an issue. A circulation that high is surpassed in this country only by the TV Times and Radio Times and, perhaps, the Reader's Digest; but, as editor Chris Donald states, that "doesn't count".

We may also remark on the low profile assumed by Chris Donald despite the fact that he is responsible for one of the larger features in the contemporary cultural landscape. After all, Piers Morgan could not resist the urge to self-promote despite the fact that the Daily Mirror haemorrhaged readers under his editorship; perhaps there is a connection.

That said, Viz no longer sells a million copies per issue. It's down to about a quarter of a million now, which some would say is a catastrophic decline, but which is generally accepted by the magazine's owners as more realistic, and still an improvement over the first issue's circulation of 150. Donald was approached by his publisher, John Brown, to write his story at the height of Viz's success; but, says Donald, "I don't believe in the opportunist, cash-in autobiography... for me the most interesting part of Brian Clough's autobiography would not be the glory days... I'd want to read the bit where he ended up in a neighbour's hedge, pissed as a fart."

And so, in Rude Kids, we get to read of Donald's life as overwork and the discouraging business of being able to afford anything you like - such as a hugely superior train set - lead him into depression. "Around this time" - as Viz's strips appeared to be descending into mere formula - "I started drinking to help me feel more morose." As it turns out, his idea of heavy drinking is "two or three cans of beer a night after the kids had gone to bed, and a large whisky chaser or two." Unlike a doctor who automatically doubles a patient's evaluation of how much he drinks, I am happy to take Donald's at face value. For all that Viz looks like it was not only conceived but put together in a pub, it is put together by people of almost monastic temperance.

Nor should you expect anything else. Donald is at pains to point out how hardworking they are. For most of its existence, Viz came out once every two months, which I always assumed was a pretty agreeable work-rate. It turns out that it's quite a lot if there are only four of you and you're pasting the magazine up with cow gum in the same bedroom you've lived in since childhood. (They were still putting Viz together in Donald's bedroom in 1988, when sales were around half a million.)

And meanwhile, you and your collaborators are at the top of your game and continually improving. The essence of good comedy is alertness, an understanding that getting the details right about what you are satirising is crucial. Some Viz strips look as though they're slapdash, but they're almost always not. In particular, those by Simon Thorp and Davey Jones merit endless re-readings. (One of the nice things about Rude Kids is that we can now put faces and characters to the strips' previously anonymous creators.) The recent one-off strip by Jones, a homage to Mad magazine that skewered the pretensions of Mel Gibson's film about Jesus, was in my opinion probably the funniest comic strip ever drawn, or at least the one that has most repeatedly reduced me to tears. (Basically, a soppy-eyed but otherwise mute and dignified Christ, already burdened with his own crucifix, undergoes further sufferings: stepping on a rake, being inflated with helium, crashing through plate glass, getting covered in itching powder, etc. It might not sound funny in paraphrase, but it is a hilarious exposure of Gibson's intent, just shy of blasphemy, and a salute to the slapstick conventions of its own medium.)

In the case of Thorp, there is an attention to and respect for detail, in both artwork and script which, as he and the other cartoonists get better, give the lie to the old claim (first voiced by The Fall's Mark E Smith in about 1986) that Viz, like Punch, was not as funny as it used to be. Early Viz relied more on puerile shock, outrage, and building-block satire to get its laughs; these days, when a strip is funny, it is funnier than anything else being produced in this country, in any medium. One might not have imagined, for instance, that a strip with the baldly descriptive title "Mrs Brady - Old Lady", initially not much more than a sour swipe at female pensioners who witter on in shops and bus queues, could have become such a strikingly rich satire on age itself, and even on death: Mrs Brady is now a lovingly drawn Struldbrugg, a Beckett heroine with a hilariously comprehensive medical vocabulary, a mixture of bald official terminology and prewar euphemism which, in combination, become more stomach-turning than any crude description of prolapsed uteri, weeping cysts and hideously involved bowel complaints. The way the writers insert a word like "oxters" at just the right comic moment shows quite how alert they are to linguistic usage; how quick they are to pounce on its comedy, like an uninhibited Alan Bennett.

After reading William Cook's book, we learn from Thorp that Mrs Brady is written like this: "We just sit Graham [Dury] down and say, "right, talk like an old lady," and off he goes." Mrs Brady is drawn by Thorp, who is - according to Chris Donald, quoted in Cook's account - "the best drawer of us by miles". Indeed it's hard not to conclude, after looking at the full-page drawing reproduced in 25 Years of Viz , that Thorp is the best comic draughtsman this country has produced since Hogarth. (Only Steve Bell and Martin Rowson come close, but their intentions are different.)

It's in the relationship between Hogarth and Viz that you begin to appreciate the magazine's worth. What we have is nothing less than a manifestation of the comic spirit which seems somehow connected with the very territory of these islands. Take, for example, the free poster map of Britain included with an issue a couple of years ago. Entitled "The Shittish Isles", it was a act of glorious anti-patriotism: every inch of the map was populated with puking, fucking, wanking, drink ing, horrible behaviour. (It's reproduced in Cook's book; use a magnifying glass.) The sea itself is surrounded by faeces and used condoms; the illustrators have appropriated the notion that something about this country - the way its class system works, its appetite for squalor, its capacity for self-destruction and relish for mindlessness - means that Gin Lane is never very far around the corner. It is not a pretty sight; but you will not find it sketched so accurately as in Viz's pages.

It is easy to think that if you wanted to give a foreigner an accurate account of what this country was like, and you were not interested in making a good impression, a few back copies of Viz would suffice. You will not learn, however, from Donald's book what it is in his head that has led him to inspire such geniuses. We are told that Mr Logic was taken from his brother's Spock-like behaviour; "It wasn't until years later we discovered the real name for it was Asperger's syndrome." Not that that has prevented Mr Logic from still appearing.

But as for clues to what makes Donald tick, we are in the dark. He is a train-spotter; he likes to settle scores (and good luck to him - when you read of some of the travesties foisted on him by marketing people and TV companies, you will weep with rage on his behalf); but the book's prose is a kind of continuous forward defensive prod, rather than the breathtaking sloshes or the beautifully deft jabs you see in the magazine. (Were tabloidese and the Iraq war ever more economically satirised than when Saddam Hussein was described as being responsible for "a war he was too cowardly even to start"?) I use the cricket metaphor, incidentally, as it is one of Donald's own habits, and internal evidence suggests he is winningly fond of the game. So get the book if you're a Viz fan - but don't expect too much typical Viz humour; more a laconic frankness. Cook's 25 Years of Viz contains similar information but has plenty of illustrations. Take your pick. Meanwhile, we await the day when a statue is erected, fnarr fnarr, to Chris Donald in the centre of Newcastle.